Due to drawbacks of semiconductor process technology, a non-volatile memory device can be flawed with a severed bitline or a short circuit developed between two adjacent bitlines. For example, given the ever-decreasing dimensions of non-volatile memory devices, two adjacent bitlines are becoming closer to each other. A short circuit can develop during a manufacturing process, because a bitline contact window is likely to occur, and adjacent bitlines are excessively close to each other.
Therefore, at the end of the manufacturing process, non-volatile memory devices have to be tested in order to confirm that charge has been appropriately injected by a programmed operation into memory cells. Non-volatile memory devices are usually tested by a verification operation process to determine whether they are defective. However, the verification operation process is so lengthy and time-consuming that a defect has to be tested repeatedly in several instances before the defect can be confirmed.